The present invention relates to an arrangement for the predictive discrete-time adaptive on-off control of continuous-time processes with binary switching actuators.
Controllers with binary switching actuators excel in their reliability and robustness. Parameter adjustment of conventional switching on-off controllers is based on the results of empirical investigations on standardized model processes specified by simple parameters. Due to the non-linearity of the controller an analytical determination of its parameters for an optimal control in the sense of an optimization criterion can be done only with very high effort.
Difficulties in finding suitable controller parameters occur especially in cases where the process to be controlled is not described precisely enough by the parameters of the respective standardized model process or in cases where its dynamics are not sufficiently known or time-variant.
Within the last decades adaptive controllers have been developed which are--contrary to controllers with fixed parameters--able to adapt to the momentary operating conditions of the process to be controlled, thus increasing the quality of control of processes that are insufficiently known or time-variant. By means of known parameter estimation methods a process model is determined and used for finding out and establishing a way of control which is optimal in the sense of a quality criterion.
The adaptive design methods known until recently are based on the assumption that the controller is able to generate any actuating signal level within the actuating range. Therefore they cannot be applied directly for the design of an adjustable control arrangement in on-off controllers, which allow only two possible switching levels. Concepts of such discrete-time adaptive control arrangements as improved so that they can have two switching levels as process input, have been known and realized for several years. For the determination of the on-off actuating signal, here, a prediction of process output sequences over several future sampling intervals as reaction to possible process input sequences is used to estimate the parameters by means of a parameter estimation method and update them in every sampling interval in order to adapt the process model to the process to be controlled, even when the process behaviour changes (Breddermann, R.: Realization and Application of a Selftuning On-Off Controller. Proceedings of the International Symposium on Adaptive Systems, Bochum, FRG, 1980, and Hoffmann, U.; Breddermann, R.: Entwicklung und Erprobung eines Konzepts zur adaptiven Zweipunktregelung, in: Regelungstechnik 29. Jahrgang, 1981, no. 6, pp. 212-213).
Said publications describe a prior art of the invention which up to now has been an imperfect realization of a concept for adaptive switching on-off control which is still to be improved. The realization of the prior art requires a high technical effort. The complex control arrangement has to be operated by highly qualified staff. The control performance documented in the publication mentioned first has a problem of excessive overshooting of the process output in the start-up phase of the process or after setpoint changes which the process is to follow. This problem is normally undesired and even intolerable, in many applications.